Combustion control



J1me 1942- G. A. BROOKE, JR, ET AL 2,285,564

COMBUSTION .CONTROL Filed April 10, 1939 2 Sheets-Sheet l INVENTORS e fZBrooite Jr 6. Chambers Gear 4. Car

June 9, 1942. a. A. BROOKE. JR., ETAL COMBUSTION .CONTROL Filed April 10, 1939 2 Sheets-Sheet 2 C5: lab H I w WESSES INYENTORS: 0514494 LE5 507 e :ZBroake W xrronmzvs.

Patented June 9, 1942 2,285,564 COMBUSTION CONTROL George A. Brooke, Jr.,

Chambers, Lanad Eng e owne, Company, Inc., 1'

Philadelphia,

Pa, assignors to Brooke and Carl C.

hiladelphia, PL.

a corporation of Pennsyl Application April 10, 1939, Serial No.

This invention relates to combustion control, and is especially advantageous for furnaces using fluid fuel or the like, such as gas, oil, or powdered coal. The invention permits of controlling combustion fluid (whether fuel or air, or both) according to the quality or character of the furnace gases, in a reliable, accurate, and satisfactory manner, and without continual overaction and reaction of the control, such as is commonly termed hunting." The control can be eflected electrically, substantially without any moving directly involved in moving the means which directly control the combustion fluid supply. I have hereinafter explained an embodiment of the invention as applied to control the supply of air, though it may if desired be applied to control the supply of fuel.

It has long been understoodthat the quality of character of the stack or flue gases from a fire in a furnace varies according to the conditions of combustion in the furnace. If the supply of air or oxygen for combustion of the fuel is deficient, the furnace gases contain an unduly large proportion of products resulting from incomplete combustion of the fuel, and even a certain proportion of unburned fuel, while their proportion of the products of,complete combustion is unduly low. In the case of carbonaceous fuels such as wood and the like, coal, oil, natural gas or producer gas-i. e., practically all com- A furnace gases from complete in CO: (carbon dioxide) contain almost no CO (carbon monoxide), contain very little free oxygen, and are nearly colorless; while the gases from incomplete combustion due to deficiency of air and oxygen contain less CO2, more CO, and a proportion of unburned carbon particles, which characteristically darken the smoke more or less, according to the degree of air deficiency in the fire. In cases of excessive air supply, the furnace gases are likewise relatively deficient in C02 because of the presence of more free oxygen in them, but are white or nearly colorless as they issue from the stack into the atmosphere.

For most commercial purposes, complete combustion without excess of air is the desirable condition; although for some industrial purposes, combustion with a deficiency or an excess of air mercial fuels-the combustion are rich sired condition gives rise to furnace gases of definite quality from the desired conditions of combustion proof the furnace gases of variation duces changes in the quality whence the fact and the direction 1 ly radiating source lamp) to pass through a definite stream (deficiency or excess of air as compared with the desired norm) is readily determined.

It has been proposed to take advantage of these facts to regulate the conditions of combustion b and according to the quality or the furnace gases; by allowing the radiation from a uniform- (e. g. an incandescent electric of the gases and fall upon a sensitive responsive device (such as an emission type photo-cell), and utilizing the electrical output or-eflect from this device to regulate the supply of combustion fluid (air or fuel) to 'the furnace. In the case of a steam boiler furnace, the uptake or outlet flue by which the spent gases are led from the heating surfaces of the boiler to the stack or chimney usually affords the most convenient stream of gases for the purpose. while such regulation has not proved practically satisfactory for a variety of reasons which it is not here necessary to discuss, we have devised a regulatory method and system of this character which in practice operate successfully and satisfactorily. Various important features and advantages of the invention will appear from the following description of a species or form of embodiment thereof, and from the drawings. Indeed, all the features and combinations shown or described are of our invention, so far as novel over the prior art.

In the drawings, Fig.1 is a general diagrammatic view of a control system for a furnace, conveniently embodying the invention; Fig. II is a fragmentary diagrammatic view illustrating a modification; Fig. is a fragmentary diagrammatic view illustrating yet another modification: and Fig. IV is a fragmentary diagrammatic view illustrating a modification involving other parts of the system.

Fig. I illustrates the application of our invention to a furnace l0 fired with fluid fuel, for example, powdered coal. As here indicated, the coal is supplied through a conduit H to a pulverizer If. The air for combustion is supplied from any suitable source, such as a centrifugal blower l3, through a conduit ll whose (smaller) primary or carrying air to the pulverizer l2, whence the mingled air and fuel pass through a conduit I! to the furnace "I, while the (larger) branch Nb of conduit II delivers secondary air for combustion directly to the combustion chamber of the furnace It, as usual. The (spent) furnace gases or products of Hi through the flue The amount of fuel supplied to thence to the furnace II) or uptake It. the pulverizer l2 (and nism A responsive to the demand on the furnace H! or the output therefrom.

As here shown, the furnace I isa steam boiler furnace, and the fuel supply control system A is load on the boiler responsive to the demand or furnace and to the output or supply of steam therefrom, as represented by the pressure in the steam pipe or manifold 20. For operating the fuel control 1, the system A-may include electromagnetic means, such as motor 2|, with connections such as reduction gearing 22, a crank 23 on the last shaft of the gear train, and a link 24 connected to the fuel control arm l1; and the electro-magnet means may be controlled by a pressure device 26 directly actuated by and responsive to the steam pressure in the pipe or manifold20, to which it is connected by a valved pipe line 21. As shown, the pressure devise 26 actuates an adjustably weighed switch lever 26 coacting with contacts 29, 29 to close the circuit 30 for the motor 2| and operate the same one way or the other to open or close the fuel control H. The motor circuit 36 may be connected to any suitable source of energization, such as an ordinary 110-volt 60- cycle A. C. light or power circuit P, shown as having one side grounded at 12. As shown, there is a follow-up connection for opening the switch 28 and putting the motor 2| out of action after the fuel control I! has been sufliciently opened or closed, comprising a lever 32 fulcrumed at 33 and connected by a link 34 to the crank arm 23, and also connected to the lever 28 through a connection including a helical tension spring 35. The helical tension spring 35 opposes the action of the pressure device 26 in response to increased pressure, and vice-versa. The'tension in the spring is reduced by operation of the motor2| and movement of the crank arm 23 to increase the fuel supply, and is increased by the reverse oper ation and movement of these parts. supply of fuel to the furnace is increased or reduced according to the relation between the demand and the output of the furnace, as represented by the steam pressure in the pipe 20.

While any of the supplies of combustion fluid (fuel or air) to the furnace l0 may be controlled by the quality or character of the (spent) furnace gases in the fine or uptake I6, in the present instance it is the supply of air that is so con-- trolled. As shown in Fig. I the air supply is controlled jointly by the quality of the furnace gases, through a unit D responsive thereto, and by the relation between demand and output affecting the furnace I0, as represented by the steam pressure in the pipe 20. The system of mechanism B wherebythe steam pressure acts on the air damper l6 may be largely similar to the control system A for operating the fuel control I1, and its corresponding parts and features are marked with the same referencenumerals (with the addition of a letter for purposesof distinction), in order to dispense with repetitive description. As here shown, the link-rod 24a of this mechanism B 31 to the damper I6. 0 through which the is pivotally connected at The system of mechanism Thus the aaeascc trie motor 40 acting through a train of reduction a reversible electric I as the steam pressure device 26a.

- to produce an overaction (in of the smoke flue l6,

gearing 4 2 to turna crank arm 43 that is" connected to the lever 26a through a connection including a helical tension spring 44. spring 3511, the spring 44 opposes the pressure device 26a. The energization of the motor cirthe motor 40 one way or the by the unit D through means such as hereinafter described.

When the air supply to the furnace I0 is less than required for the bustion,

ditional effect on the lever spring 44, as by means of a fan on the motor shaft arranged to blow or suck air (according to the direction of rotation of the motor) into or out of the open mouth of a T-fitting 5| at the end of a pipe line 52 connected to a pressure diaphragm device 53 acting on the lever 28a as well As already stated, this fan 50 is so arranged that its energization of the pressure device 53 tends to produce the same effect as the spring 44or, in other words,to exaggerate the effect of a slight change of tension in the spring-thus causing the switch 28a to close and bring the motor 2|a into action more readily. The fan 50 and the quality of the furnace gases, and may even tend excess of that properly due to the spring 44) which will be corrected by the latter as soon as the motor 40 stops and the pressure device 53 is thus de-energized. so as to be no longer effective on the lever 26a.

As here shown, all of the motor circuits 30, 30a

' device D comprises a source of radiation 55, such as an incandescent electric lamp, device or cell 56, such as an emission type photocell or any suitable type of electric eye. The radiation source 55 is shown arranged at one side so that its rays'traversing the smoke or furnace gases in said flue fall on the device 56 directly across the flue.

and a sensitive The output or :the device 55 (preferably against opposing electromotive force, and utiafter amplification) lizing the resultant to control the direction of action and duration of the current in the motor circuit 55, and the resulting effective speed of the motor 45. The unit D is shown in Fig. I as including an amplifier d-of vacuum-tube type (e. g.,

a triode) for amplifyingthe small electrical output or voltage of the cell 55 due to excitation by the rays from the source 55, and-there are associated with this unit D a balancing system E receiving the amplified output or voltage from said unit D and a further amplifying and control system F for supplying current to the motor circuit 55 to operate the motor 45 one wayor the other.

Power for the unit D, for the systems E and F, and for operating the motor 55 may be supplied from the power line P through leads" 55, having branches 65a, 55b, 50c and 5|a, 5|b and He, respectively. The lead 55 being connected to the grounded side of the power circuit P, it follows that all points on the circuit branches 55a, 55b, 550 are grounded. As shown in Fig. I, the source of radiation 55 is connected across the power circuit branch 50a, 5|a, an adjustable calibrating resistance 52 being interposed adjacent the device 55. The cathode of the triode vacuum tube d is connected in a circuit 54, between resistances 55v and 55 therein, and this circuit 54 is connected across the circuit branches 55a, Ho. The plate of the vacuum tube d is connected as hereinafter described to the branch 55b of the lead 55, while its grid is connected through a lead 51 including a resistance 55 to a shiftable point on the resistside of the sensitive device or cell 55 is connected by a lead to the circuit 51, between its resistance 55 and the grid of the tube d, so as to feed the cell voltage to the grid. By shifting the connection of the circuit 51 along the resistance 55, the current through the tube d between the circuits 5% and Na and through the primary of the transformer 1| may be kept in desired phase relation with the current through the circuit (Nb and the primary of the transformer 12.

The balancing system E shown inFig. 1' comprises transformers 1| and 12 connected as hereinafter described. The primary of the transformer 1| is connected between the circuit branch 55!) and a lead 15 from the plate of the tube d, whose cathode is connected to the circuit branch 5|a through the side of circuit 54 that includes resistance 55. Accordingly, impulses amplified under control of the sensitive device 55 traverse the transformer primary. The primary of the transformer 12 is connected between the circuit branch 50c and the circuit branch Gib, and adjustable resistance 14 being interposed in this latter connection. The secondaries of the transformers 1| and 12 are connected in a loop circuit 15, which includes a resistance 15 in one side of the loop. The other side of the loop 15 is connected by a lead 11 to the circuit branch 550. A point shiftable along the resistance 15 is connected by a lead 15 including a resistance 18 to a point of the circuit 55c further from the transformer 12 than the connection of the lead 11 to said circuit 55c. By adjusting the resistance 15, the system is calibrated roughly to balance the impulses in circuit 15 (due to the A. C. impulses in the primary of transformer 12 against the opposing impulses in said circuit due to the impulses in the primary of transformer 1| (from the sensitive device 55 and tube d) when the quality of the furnace gases in fiue i5 corresponds substantially or approximately to the desired conditions of combustion. A finer calibration may be made by adjusting the connection 15 along the resistance 15.

The phase relation between the impulses in the primary of transformer 1| and the A. C. current in the primary of transformer 12 should be or such that the resulting A. C. impulses or currents in the secondaries of these transformers essentially balance one another when the quality of the fiue gases at I5 is that desired-neglecting minor irregularities of the A. C. in the secondary of transformer 1| (due to the fact that it is produced by unidirectional impulses in its primary, rather than by A. C.), which are damped out in the system F as hereinafter described. Under this condition; points on the resistance 15 at one side of the connection 15 are always plus when points on said resistance 15 at the other side of said connection 15 are minus, and vice versa. As long as the quality of the flue gases at I5 is just as desired, there is essentially no voltage or flow in th lead 15; but whenever the quality deviates from the desired, there is a differential or signal (voltage and electrical impulses) one way or the other in said lead 15, according to the magnitude and character of the deviation, which is transmitted to the system F as hereinafter described. signal impulses varies according former 1| or that from transformer 12 predominates in producing them, i. e., according to which way the quality of the furnace gases deviates from the desired normal.

As here shown, stages of amplification, which may be effected by g and h. The tube g is shown as a triple grid detector amplifier, while the tube It is shown as a single grid detector amplifier. The system F here shown also comprises two alternatively acting agencies for supplying unidirectional current impulses, such as grid glow tube rectifiers 9' and k of Thyratron" type, which may receive the output of amplifier h through a transformer t, and are shown connected to feed the leads of the motor circuit 45. To provide the required plate voltages for the tubes 9 and h, the system F may include a rectifier, shown as a vacuum tube m.

The system F may receive power from the circuit P through a transformer 55 whose primary is connected between the circuit branches 550, He, and whose secondary is in sections. The first section of the transformer secondary is connected in a heating circuit 5| with branches to the heaters of the indirectly heated cathodes of vacuum tubes 9 and h. The second section of the transformer secondary is connected in a heating circuit 52 with branches leading to the heaters of the indirectly heated cathodes of the tubes and k, one side of this circuit 52 including a portion of the grounded circuit branch 50c, and being thus grounded. The third section of the transformer secondary is connected in a circuit 53, which is further described hereinafter. The fourth section of the transformer secondary is connected in the heating circuit 84 of a vacuum tube m whose cathode heaters are in series with one another and whose anode plates are shown connected to the circuit branch 5|c in parallel. The mid-point of the first section of the transformer secondary is shown as connected to the (grounded) circuit branch "0 by a lead 55; and the circuit 55 of the third transformer the system F involves two.

' to the circuit section is shown able resistance 88.

branch 600. for the tubes g and h may be the Thyratro'n Ill including condensers H2, H3 and resistances H4, H5, respectively. Intermediateiy, at its midis impressed across or mary of the transformer t.

2,285,664 as including an adjustable variflue l8 and the resulting output voltage oi the sensitive device 56. The phase of this ot'the tubes with either limit-switch 54 of the reduced the signal tube :1 or is thus ceasesflring and the motor 40 stops,

If after such discharge the tube 7' or k resumes firing and runs again, a' negative charge will the critical value.

As the corrective periodically involved instead of the tube 7.

or even absolutely. Thus or speed of corrective action on the will he graduated according to the magnitude of the signal voltage. It may even happen, ind that the pulsations of energy supply to the motor 40 may be of such great frequency that the motor will virtually run more or less continuously, but at gradually diminishing speed.

The feed-back :i: is intended to be so calibrated or adjusted that the motor will be operated in such a way as to compensate for the action on the quality and to prevent overtravel of the motor after mine. 88 more fully explained hereinafter. Thus the corrective system C can be operated rapidly to restore approximately the desired conditions of combustion, without danger of overcorrection and hunting in the final flner correction.

To secure the desired action the feed-back a: as described above. suitable relations must exist amongst the capacities C of the condensers H2, H3, I22 and the values R of the resistances H1, H8, 12!: Cll2xR.lI1" Cl22xRi2l CHSXRIIB: in other words,, CH3 RI|8 are each Cl22 Rl2L Under these conditions, the condenser H2- or H3 will discharge more rapidly than the condenser I22, and the voltages V across the discharging condensers will change in'llke manner. Accordingly, the bias on the grid of the tube 1, which is (VIII-VI II), will increase negatively during the discharge of the condensers H2 and I22, so thats signal voltage higher and higher above the critical voltage for firing required to make the tube a continue firing. However, the condenser H2 will reach a condition of substantially complete discharge before the condenser I22 does; and so there-will be a point beyond which the condenser I22 will discharge more rapidly than the condenser ill. After this point, the negative bias on .the grid of the tube a'- will decrease, and a point may be reached at which the'signal voltage may sumciently counteract the, voltage due to the feedback a: to cause the tubefi' to resume the motor Ill to operate again awhile, until again stopped by similar feed-back action. Hence the supply of energy interrupted, or, pulsated. Thus the correctibi of tion conditions in the furnace it proceeds intermittently with pauses during which the change may make itself sufficiently felt in the system signal voltage imtransformer t below g the tube 7'. f the tube It is and longer, relatively, the effective or net rate of operation the motor 40 and its pulses in the primary of the the critical value for course the action is similar when Fig. II illustrates a modification in which the it is here controlled entirely by the totally unaffected CIIIXRIH and firing, and s this tube will be i to the motor units D and E of the control system,

by the steam pressure. In other respects, the is the same as already explained in features reference numerals as in tive letter added, necessary) in order to dispense description.

F18. III shows a feature the regulatory system of Figs. I and II, but is illustrated separately in orderto avoid confusion. Accordingly, various parts and features are marked with the same reference numerals as in Fig. I (with a distinctive letter added, where such distinction appears necessary) as a means of dispensing with repetitive description.

As shown in Fig. III, the connection 18 of Fig. I includes a contact arm lie that is automatically moved along the resistance It by a link-rod connection c from the crank 43, which is operated by the motor 40. This results in a followup action tendin to reduce the ll operates to correct the given However, the system of Figs. I and II is fully operative as hereinbefore described without the follow-up feature of Fig. III.

Fig. IV illustrates a modification, involving the wherein the opposing electro-motive force against which the output or voltage of the device 56 is balanced is provided in a different way from that shown in Fig. 1. For this purpose, besides the sensitive device 56, the unit I) includes a similar or counterpart sensitive device or cell 56d exposed directly to the radiation from the source of radiation (preferably the very same source that affects the device 56), without the intervention of there is an amplifier dd similar to the device 5|, with similar connections and resistances Md, 65d, 86d, 61d, Bad, to the sand Bid; and the two sides of the device d are connected (like those of the device 58) Fig. where such distinction appears with repetitive 10d) to the corresponding circuit 61d. sensitive devices 56, 56d are subject to radiation from the same source 55, and are therefore affected just alike by voltage fluctuations or other variations affecting this source; and they have identical parallel circuit connections, including counterpart amplifiers d and dd. As regards efl'ects on the devices 5!, 56d, fluctuations of the source 55 balance perfectly; so that only variations in the quality of the gases at It affect the system.

The balancing system E shown in Fig. IV comprises a resistance 1 Id that is connected between the circuit branch 0b plate of the tube d, and a resistance 12d that is connected in a loop with the secondary of a phasedisplacing or reversing transformer 10 whose primary is connected through a resistance r between the circuit branch Gllb and the lead 13d from the plate of the tube dd. The resistance r plus that of the transformer primary should be equal in value to the resistance lid. As shown, the resistance 12d and the secondary of the transformer w are both connected to the lead 60b. The resistance 1 Id and 12d are connected in a balancing loop circuit 15d that includes the lead Bill) as one side of the loop and a resistance 16d at the other side of the loop. As shown, the connections of the resistance lid to them are shiftable or adjustable along the resistances I id, 12d, which are thus in effect potentiometer rewhich is applicable to signal voltage as combustion alead and the lead 13 from the opens the signal circuit sistances. Froma point shittable along the resensitive-cell controlled by the quality of the furs istonce 'lldexten theconnection 18d (through nace gases, the combination with a source 01' whose adrays and asensitive cell xposed to rays from the furnace I II, the relay switch I25 connection 18d (to the system I), so that continued operation or the other tubed shall not result in shutting off the i supply of combustion fluid said source and I bustion fluid to a furnace by means including a sensitive cell controlled by the quality 01 the iurnace gases, said Point. shit ce, is connected to the table along said reamplifying system.

GEORGE A. BROOKE. JR. cam. c. emmanas. 

